A bicycle, which is used as one of land transportation means, is basically driven by a user's driving force, so it is very useful in terms of environment pollution prevention and energy saving. The bicycle may contribute to enhancing a user's physical strength, so the bicycle is very popular since it can used as a leisure activity tool. More specifically, the bicycle may be used as a transportation means and a sport or leisure tool. Such a bicycle may be categorized into many different types based on the purpose of use, structure, material, driving principle, etc.
In terms of the purpose of use, the bicycle may be categorized into a common type, a racing type, a MTB type, a leisure type, etc. In case of the common type, the bicycle may be categorized into a bicycle for one user, a bicycle for two or more than two users, and a bicycle for freight.
In terms of the structure, the bicycle may be categorized into various types based on the reference of categorization. For example, the bicycle may be categorized into a folding bicycle and a non-folding bicycle based on the presence of a foldable body.
In addition, the bicycle may be categorized based on the materials of the body frame, for example, a cold-rolled steel plate, a stainless steel, a chrome-molybdenum steel, aluminum, titanium, magnesium, a carbon fiber, etc. In particular, the weight of the material of the body frame accounts for almost the total weight of the bicycle. For example, assuming that the inclusion ratio of the chrome-molybdenum steel is 100, the ratio of titanium is 50, the ratio of aluminum is 34, and the ratio of carbon is 18, which means that the bicycle having a body frame made of a carbon material is lighter than the bicycle made of other materials.
As mentioned above, the bicycle may be categorized into a variety of types based on the reference of categorization. For the sake of easier understanding of the present invention, the bicycle may be categorized into a classical type bicycle and a modern type bicycle based on the outer appearance of the body frame. Throughout the descriptions of the present invention, the bicycle will be roughly categorized into a classical type bicycle wherein a head tube, a top tube, a bottom tube, a seat tube, a rear tube, a chain tube, etc. which are all belonging to the body frame of the bicycle are made of circular pipes, and the connection portions of each tube are welded or connected using a separate connection member, and a modern type bicycle wherein the diameter or thickness of each tube belonging to the body frame is relatively larger or thicker than each of the tubes of the classical bicycle, and each tube is configured in a variety of designs, not in a circular pipe shape. This categorization is made based on the facts that the body frame of the classical bicycle is mainly made of metallic circular pipes wherein iron is contained as a main composition, and the body frame of the modern style bicycle is mainly made of new materials, for example, a carbon material, based on the purpose of use, so the modern style bicycle can be made in various designs.
FIG. 1 is a view illustrating an example of a conventional classical type bicycle 10. There are provided a top tube 12, a bottom tube 13, a seat tube 14, etc. which form a body frame 11. The diameters of such tubes may be minutely different, but they are mainly made of circular pipes. Such a classical type bicycle is being used as a common type or racing type bicycle rather than a MTB or leisure type bicycle. In particular, the bicycle wherein the body frame 11 is made of a metallic material, for example, steel, aluminum, etc. used as a main composition.
FIG. 2 is a view illustrating an example of the conventional modern type bicycle 20. The top tube 22, the bottom tube 23, the seat tube 24, etc. which form the body frame 21 have different thicknesses. Such tubes all are integrally molded or partially molded and are assembled through a separate assembling process rather than the tubes are manufactured by connecting circular pipes. In particular, the above modern type bicycle mainly corresponds to the MTB or leisure bicycle wherein the body frame 21 is made of a carbon material.
As illustrated in FIGS. 1 and 2, the classical type bicycle 10 and the modern type bicycle 20 have key differences in the outer diameters (or thicknesses) of each tube belonging to the body frames 11 and 21. More specifically, each of the tubes 12, 13 and 14 of the classical type bicycle 10 have relatively smaller outer diameters (or thicknesses) as compared with the tubes 22, 23 and 24 of the modern type bicycle 20. Since the body frame 11 of the classical type bicycle 10 is made of metallic circular pipes, even when the diameters are large, the strengths are high, whereas the body frame 21 of the modern type bicycle 20 is mainly manufactured through the molding process by using a carbon material, so the outer diameters (or thicknesses) should be relatively larger so as to secure enough strength.
Of course, the reason why the tubes 22, 23 and 24 of the body frame 21 of the modern type bicycle 20 are made thicker is not because of their materials. Such tubes should be made thicker in an effort to provide more active, strong and stylus impressions when designing the MTB or leisure bicycle.
Meanwhile, as illustrated in FIG. 1, a top tube 12 and a bottom tube 13 are formed in a triangular shape and about a seat tube 14 at a front end of the body frame of the classical type bicycle, and a rear tube 15 and a chain tube 16 are formed in a triangular shape at a rear end thereof, which consequently looks like a diamond shape. In such a body frame 11, relatively more torsion stress may concentrate at a front portion 12a of the top tube 12, a front portion 13a of the bottom tube 13, a lower portion of the seat tube 14, etc while a user is riding the bicycle. As illustrated in FIG. 2, a front portion 22a of the top tube 22, a front portion 23a of the bottom tube 23, and a lower portion of the seat tube 24 are made relatively thicker in the body frame of the morn type bicycle.
Since the classical type bicycle in general is made by connecting circular metallic pipes, the tubes belonging to the body frame has roughly same outer diameters at the front and rear portions (or upper and lower portions). In addition, in case of the modern type bicycle wherein the body frame is made using a carbon material, since it is easy to make different the thicknesses of the front and rear portions (or upper and lower portions) of the tubes, the body frames can be manufactured in various designs.
So far, there has not been any trial to make a frame body of a bicycle using a carbon material while maintaining a traditional design of tubes belonging to the body frame of the bicycle. In addition, since the main frame of the classical type bicycle is made of metals, the weight is very heavy, so it is hard for the user to handle it.